Calorimetric Evidence for Pauli-Paramagnetic Superconductivity

Specific-heat measurements at $0\le H\le 29\mathrm{kG}$, $0.33\le \frac{T}{T_c}\le 1$, on the extreme (${\kappa }_G\approx 67$) type-II superconducting alloy Ti-16 at.% Mo (previously shown to display reversible paramagnetic magnetization in the superconducting mixed state) (1) confirm the second-order nature of the upper-critical-field transition between the paramagnetic mixed and paramagnetic normal states at $H_u\mathrm{}\left(T\right)\mathrm{}$ down to $\frac{T}{T_c}=0.76\mathrm{}$, (2) show that the mixed state remains a single thermodynamic phase in the paramagnetic region, and (3) indicate that ${\kappa }_1\equiv \frac{H_u}{\sqrt{2}{H}_c}$ and ${\kappa }_2\propto \left\{\frac{\partial \left[4\mathrm{}\pi \right(M_S-M_N\left)\right]}{\partial H}\right\}_{H_u}^{}{}_{}{}^{\frac{-1\mathrm{}}{2}}$ (where $H_c$ is the thermodynamic critical field, and $M_S$ and $M_N$ are superconducting mixed-state and normal-state magnetizations), both decrease with decrease of $T$.